1. Field of the Invention
The present invention relates to a method of forming a metal oxide film on the surface of a substrate such as a plastic substrate and a microwave power source device used for the above method.
2. Description of the Related Art
In order to improve properties of various substrates, it has heretofore been attempted to form a metal oxide film on the surfaces of the substrates.
In the field of packaging materials, for example, it has been known to form a metal oxide film on a plastic substrate such as of a container by, for example, a plasma CVD method to improve the gas-barrier property. A method of forming a silicon oxide film (SiOx) has already been known (see, following patent documents).
[Patent Document 1]
Japanese Unexamined Utility Model Publication (Kokai) No. 50563/1974
[Patent Document 2]
Japanese Unexamined Patent Publication (Kokai) No. 58171/1974
[Patent Document 3]
Japanese Unexamined Patent Publication (Kokai) No. 345383/1993
[Patent Document 4]
Japanese Patent No. 2526766
However, the conventional metal oxide films as represented by a silicon oxide film are accompanied by such problems as lack of softness or flexibility and poor adhesion to the substrate. This tendency appears conspicuously particularly when the substrate is made of a plastic material. When the adhesion is poor, the resistance against water is weak and the film easily breaks when it is brought into contact with water making it difficult to accomplish a desired gas-barrier property and, further, deteriorating the productivity.
Besides, when a metal oxide film is formed on the surface of a plastic substrate by the microwave wave plasma CVD, overheating occurs locally and the plastic substrate is deformed.